Previous studies on immune function associated with aging in humans indicate that T-cell mediated effector functions are impaired whereas B-cell functions may not only be relatively preserved but may also escape from normal immunoregulatory control. We will study regulator cell activity directed against both T and B cell effector functions. Both mitogen activated and nonactivated regulator cell assays will be used. B-cell effector function will be assessed by radioimmunoassay of in vitro immunoglobulin (Ig) production. IgG, IgA, IgM, kero Ig and gamma Ig will be measured so that both quantitative and qualitative changes can be detected. T-cell function will be studied by cell reactivity to mitogens, antigens and mixed lymphocyte reactions. Lymphocyte membrane properties will be studied by measuring cell capping; altered membrane properties with aging may impede normal cell-cell interaction and this affect immunoregulation. These initial studies will form the baseline for attempts to restore immune function using potential therapeutic agents. We will explore whether characteristic immune dysfunction occurs within the central nervous system (CNS), a compartment in which immune dysfunction can occur without being reflected in the peripheral circulation. We will determine whether immunoglobulins with specific characteristics or specificities accumulate in the spinal fluid of the elderly. Aberrant immune function within the CNS may contribute to the increased susceptibility to infection, the accumulation of cerebral amyloid, and to the intellectual decline characteristic of the aged.